This invention relates to improvements in air rifles of the hinged barrel type in which the rear end of the barrel is hinged to the front end of the body of the rifle, so that it can be swung out of its normal or firing position to enable a pellet to be inserted into its rear end and so that it can be used as a lever for compressing a spring within the body of the rifle.
In prior hinged barrel type rifle designs wherein a fork-shaped part secures the hinged connection between the barrel casing and the compression chamber body it is known:
a) to construct the assembly of the fork member and compression chamber with only a single body obtained by a forging operation as described in German Patent No. De-A- 1,913,239. The purpose of this prior device is to obtain transfer passage of a small length communicating the compression chamber with the base of the fork member to increase the performance of the rifle by a lesser pressure loss; the technique implies the following drawbacks:
very expensive fabrication costs; PA1 compelled finishing operations; PA1 necessitates special reinforcement means in the used pistons due to the specific shape of the compression chamber obtained by forge;
b) to provide a thread connection that needs the thread cut in a cylindrical part, extending the fork, that is set on the compression chamber front end entrance, provided, on its inner wall, with a second thread cut; this solution presents the drawback of a requirement for a greatly accurate function associated with the fact that the assembly between the two parts must be vacuum-tight because any pressure decrease in the chamber generates a significant decrease in the rifle performance;
c) to provide a welded connection of the cylindrical portion, extending from the fork, that remains introduced in the entrance of the compression chamber front end, using mainly manufacturing process.
The requirements of the fork-shaped piece are to secure the vacuum-tight connection of the compression chamber end, and to allow the axis of the barrel, in firing position of the arm, to be coaxially aligned with the compression chamber air exit hole.
For this purpose several means are used:
a) devices working as a positioning stop, in firing position of the arm, comprising a locking element, obtained by an accurate finish of the surfaces in contact, in such a way that the fork bottom and the barrel casing rear face on which the part is hinged, are substantially flat:
b) devices using stops defined between a step of the casing of the barrel rear end and a second step formed by a prismatic section that constitutes a portion of the stop part for the locking element, set at the fork bottom; the faces in contact of the two stepped profiles require an accurate finish; in addition, the relative position of the two steps require very accurate calculations to guarantee, in firing position of the arm, the coaxial alignment of the pressurized air exit hole with the barrel axis requiring also further control and testing works for each part entering in the manufacturing process;
c) barrel stops constituted by a groove made on the barrel lower portion that corresponds at least with a fork cross rod, such as disclosed in the British Patent GB 941 711;
d) positioning stops constituted by a fractioncylindrical configuration that extends in the barrel casing rear portion and that is supported on a cylindrical portion located at the compression chamber front end.
All these solutions, though valid, require, in general, for their embodiment, delicate mounting operations and further very accurate finish and testing works to guarantee a perfect alignment between the barrel and the compressed air exit hole, essential works for a suitable efficiency of the rifle and making in addition possible the effectiveness of connections means set by a profile in correspondence between the fork member and the barrel rear end, making the joining area vacuum-tight, co-operating also with the pressurized air optimum efficiency.